Apparatus for polishing plate glass



Oct. 29, '1929. P CROWLEY 1,733,295

APPARATUS FOR POLISHING PLATE GLASS Filed July 27, 1923 Patented I Oct.29, 1929 UNITED STATES PATENT 'OFFICE' JOSEPH P. CROWLEY, OF TOLEDO,OHIO, ASSIGNOR TO LIBBEY-OWENS GLASS COMPANY,

OF TOLEDO, OHIO, A. CORPORATION OF OHIO APPARATUS FOR POLISHING PLATEGLASS Application led July 27, 1923. Serial No. 654,093.

This invention relates to improvements in the art of making polishedplate glass, and more particularly to a new and improved apparatus forpolishing the surfaces of flatground sheets of glass.

It has among its objects to finish fiatground plates of glass in anexpeditious and economical manner, and to eliminate or simplify varioussteps in the polishing operation.

In th'e manufacture of plate glass, it is the practically universalpractice to cement a number of the raw sheets or blanks to the surfaceof a large rotating table by means of plaster of Paris, and tothen applygrinding and polishing tools in succession to the exposed faces of thefixed sheets. After one side of the sheets has been finish-ed in thismanner, they are. pried loose, turned over, and again cemented down,after which the grinding and polishing operation is repeated. Each sheetis firstembedded in the plaster of Paris which not only cements thesheet to the table but fills up the spaces between sheets so that acontinuous surface of glass and plaster is exposed to the grinding tool.This sheet-holding table is then moved to position beneath a series ofgrinding tools or heads and the table and heads rotated about differentcenters so that the abrading action of the grinders first reduces all'of the sheets and plaster to a common level and then grinds the sheetsuntil every sheet has aeflat smooth surface suitable for polishing. 'Thetable is then removedfrom beneath the grinding tools, the exposed facesof the sheets and plastercarefully cleaned, and such portions of theplaster bed as are loose or have been broken away are replaced. Thetable is now shifted into position beneath a series of polishing headswhere the surfacing process is completed. The table is thenremoved andthe plaster broken away and the sheets pried loose. The sheets and tabletop are thoroughly washed,l after which the Isheets are reversed toexpose the unground surfaces and again plastered to the table. Thegrinding and polishing process is then repeated on the faces nowuppermost, afterL which the sheets must aga-in be broken away from theplaster and then cleaned.

Serious objections to this practice have long been recognized and willbe later apparent. The bond afforded by the plaster of Paris is notalways sufficient, in which case the loosened sheets are thrown olf bycentrifugal force with serious loss by breakage.` The cement-ing down ofthe sheets requires a very considerable amount of hard labor, as well asexpensive material. This process known as laying or seating the sheet,must be very carefully and skillfully done or the sheets will becometilted out of the horizontal and the edges of some of the sheets willproject above the common level. After laying athin covering or blanketof wet plaster on the table top the sheet is quickly laid on thisplaster, after vwhich several workmen stand on the sheet and work thesheet backwards and forwards with their feet until it has become seatedas closely and rigidly as possible in the plaster.

No matterhow skillfully this work is done it is almost impossible toseat the sheets with their upper surfaces absolutely horizontal, and theinitial engagement of the grinding or polishing tools with the moreexposed edges of the sheets is responsible for much breakage. Also thistilting tends to produce sheets of unequal thickness by grinding 0H moreglass in one part of the sheet than in another. Furthermore, even ifnone of the sheets is tilted, the plaster of Paris layer may be thinnerbeneath one sheet than another, thus producing sheets of differentthickness, although simultaneously surfaced. Also some of the raw sheetswill inevitably be thicker so that grinding must be continued to anextent suilicient to grind the thinnest or lowest sheet on the table.This use of cement to stick down kthe sheets also necessitates acleaning operation to remove the plaster of Paris film which remains toa certain extent on the original polished Y surface of the sheet afterit has been finished and pried loose for the second time. The entiremethod is quite tedious and expensive, and offers many opportunities forbreakage.

Other means for holding the sheets upon the supporting table have beenproposed, but the method described in detail above is the one now inpractically universal commercial use.

' different system of surfacing the sheets, whic sheet at a time.

is faster, more economical and produces a more uniform finished article.The system is most advantageously employed for surfacing sheets ofstandard size and shape, preferabl square. All of the edges of thesesheets or lanks are slightly beveled to avoid chipor fracturing of thesheet during thel suracing operation. Preferably, each individualgrinding or polishing machine is adapted to work upon a single sizesheet, and upon one sheet at a time, although a machine may be ada tedfor surfacing sheets of various sizes, or or surfacing more than onecued to the supporting table by plaster, but is merely placed loosely ina shallow recess in the table top, this recess preferably conform- Vingto butbeing slightly larger than the glass sheet. The surfacing tool isthen lowered so that its wei ht `rests upon the glass sheet,

and the weig t of this tool in addition to the A twistin movement whichis imparted to the sheet w en the rotation is commenced, serves to setthe `sheet firmly in the recess. When the ex osed surface of the'sheetis properly groun the sheet is taken out,'reversed, and the other l.sideground in a similar manner. This sheet now completely ground on bothsides, is transferred to a quite similar polishing "machine, where thesurfacing operation is completed. This polishing machine comprises thesubject-matter more specifically disclosed and claimed in this presentapplication. l

In the accompanying drawings:

'l Fig. 1 is a central vertical section through a ortion of one of thepolishino units.

ig. 2 is a plan view of the sheet-supportin table, on a somewhat smallerscale.

1g. 31s a vertical section through a portion of the table on an enlargedscale, taken s each pohsher comprismg a felt pad 14 sesubstantiallyonthe line 3-3 of Fig. 2.

Fi 4 is a view sinilar toFig. 3, showing a di erent form of ad'ustmentfor the toolsupplorting portions o the table.

T e sheet-supporting table lis mounted at' the upper end of column 2which turns in bearings 3 in the frame-work 4. The table is preferablysupported on suitable roller bearings 5 and is positively rotated bymeans of a large bevel gear 6 secured to column 2 and driven throughbevel pinion 7 on a drive.

shaft 8, rotated from any suitable source of ower, such as an electricmotor. The table 1s round, but carriesv upon its upper facea fiat squaresheet-supporting member 9, whose center, in the construction here shown,substantially coincides with the center of the table. This member'neednot necessarily be square, but should substantially conform to thecontour of the sheet to be surfaced on this machine. This su portingmember 9 is preferably cons tructe of heavy metal so as to be Thev sheetor blank is not seground as closely as possible to an absolute plane soas to serve as a master surface or pattern upon which the fiat groundglass sheet is firmly andevenly supported. Surrounding this squaresupporting memberl is a series of foursectors 10, also secured to thetop of 'table 1, which project somewhat higher than the upper surface ofmember 9 so that a square 4sheet-receiving recess or depression isprovided in the top of the table. A sheet- .supporting ad of yieldingmaterial 11 covers the upper ace `of member 9. The material best adaptedfor 'this purpose is cork, or a v cork composition. A cork-carpet formedof a -very compact composition of ground cork and a linseed-oil gum hasbeen found most satisfactory.` This material, although sutilcientlyyielding, is waterproof, will not warp or swell, andy willv not absorbthe rouge, used dur-ing the,polishing operation, as will paper or clothfabrics. Neither is it affected by the rather intense heat developedduring the polishing operation. This cork composition also has^a highcoefficient of friction with the glass surface.- This pad should be ofabsolutely even thickness, so that the master surface on supportingmember 9 will be repeated on the upper surface of the cork pad. Thewallsof the square recess are outlined by vertical strips 12 ofyieldable material such as rubber. The recess, the bottom of which isthe'pad 11 and the'walls of which are determined bythe yieldable strips12, conforms to but is slightly larger than, the ground ,glass blank 13which is to be polished. The

upper surfaces' of side sectors 10 project above the cork pad 11A adistance just equal tothe thickness of the ground glass blank 13, sothat the recess thus formed in the table top will have substantially,the same dimensions as the glass'blank.

The polishing tools are of standard design,

der and polishing tools from the table and glass sheetJ when thepolishing operation is completed, andlowerv the tools onto the sheetwhen a new polishing operation is to be per- .,formed. When in operativeposition the polishing tools rest with their entire weight upon theupper surfaces of the glass sheet and the side portions of thesupporting table, and are permitted free movements in the orbitdetermined by the centrally pivoted spider 18.

The polishing tools are not driven other than by the frictionalresistance offered by the rotating table and sheet upon which they rest.

As here shown, three series of these polishing heads are used. Onelarger series is so pivoted that the orbitI of travel of the polisherswill cover the center of the sheet as well as the edge portions thereof.Two other series of smaller polishers 20 are so mounted that theirorbits of travel pass completely oftl from and on to the edge portionsof the sheet, as shown more clearly in Fig. 2.

It is essential that these polishing pads be supported while off fromthe glass sheet, and

that they be'guided evenly onto and olf from ished onone of thesemachines will ordina` rily be of a uniform standard thickness, theplates 21 may ordinarily be designed of a proper-thickness, and fastenedpermanently l in place on the side sectors 10. However, to adaptv thesemachines for polishing different thicknesses of plate glass, anysuitable means `for vertically adjusting the polished side plates 21 maybe adopted, examples of which are shown in Figs. 3 and 4.

In Fig. 3, each plate 21 is provided with a series of dowels22 fittingrecesses 23 in the sectors 10. One or more suitably perforated thinshims 24 may be inserted between the polishing plate 21 and thesupporting sbctor 10, after which the plate and shims are secured'inposition by screw-bolts 25. By varying the number of shims 24 used, theplane-` of the upper tool-supporting surface of plates 21 may be made toconform exactly with the tool-supporting surface of the glass blank 13which is to be polished. Of course,the adj ustment mentioned above needonly be made at such times as the standard thickness of glass plates tobe polished is changed.

A different form of adjustment is shown in Fig. 4. In this case the4plates 21 are guided as before by dowels 22 operating in .recesses inthe supporting sectors 10. A plurality of threaded supporting bolts 26extend downwardly from plate 21 through suit-Y able apertures i'n thesector 10 and table 1,

and each is in threaded engagement with a worm-wheel 27, rotated by worm28 on a rotatable adjusting shaft 29. VBy suitably rotating shaft 29,the bolts 26 and consequently the plates'21 supported thereon may bevertically adjusted to any desired position.,o In this latterconstruction the yieldable Ledge members 12 which outline the recess inthe table may, if desired, be secured to the plates -21 so that they maybe vertically adjusted along with the polished plates. The two adjustingmeans shown in Figs. 3 and 4 are merely examples of many different waysin which these tool-supporting plates 21 may be vertically adjusted toconform to the thick- 7( ness of the glass plate to be polished.

In operation, when the machine is stationary, and the polishing heads 14and 20 are all raised above the table, a flat ground sheet or blank 13,the edges of which have been slightly beveled, will be laid looselydirectly upon the pad 11 in the table recess. When the polishing toolsare lowered onto the sheet and the table 1 is rotated, the slightshifting movement allowed the sheet in the slightly oversize recess willpermit the sheet to seat itself firmly and evenly upon the mastersupporting surface under the weight of the polishing tools. Usually, thesheet will slightly shift within the recess and wedge itself adjacentits corners against the yieldable side strips o r abutments 12, asindicated in dotted lines in Fig. 2. With the square recess arrangedsubstantially symmetrical over the axis of the table as here shown,.there is very little tendency for the sheet to be thrown from the tablewhen rotating, since the center of gravity of the sheet [will liesubstantially in the axis of rotation of the table. The frictionalcontact of sheet 13 with supporting pad 11, in combination with thewedging action of the sheets against portions of the yielding side wallsor abutments 12, is suihcient to hold the sheet firmly against lateralshifting movement after the polishing operation is once under way. Thesheet is held down against the master supporting surface by the weightof the polishing tools, aided to some extent by the inding action of theedge strips 12.

As is usual with machines of this general type, a mixture of rouge andwater is fed to the contacting surfaces of the pads 14 and thel glassblank during the polishing operation.

Since the smaller polishing pads 20 pass completely off the glass sheetwhile in the outer portion of their orbits, it is essential that they besupported during this portion of their travel, otherwise they would dropbelow the edges of the sheet and breakage would. occur when theyattempted to passv back onto the "sheet, Furthermore, in order to'secure a proper uniform polish on the edge portions of the sheet, it isessential that the upper supporting surfaces of vmembers 21 practicallycoincide with the supporting surface of: the glass sheet` as outlined inthe previous description. Furthermore, if there is any directengagementbetween the edges I of the glasssxblan-k 13 and the felt polishing padsas the pads pass onto the sheet, the cakedv rouge on these pads, whichis essential to the polishing operation,will be scraped away, and thepads will also be quickly cut to pieces by the sharp edges of the sheet.'15

With the edge-supporting plates 21 arranged as above described, no suchengagement takes place, and the polishing tools are guided evenly ontoand off from the sheet without injury to either the pads 0r the glasssheet being operated upon.

` l/Vhen one face of the sheet 13 is properly polished, the polishingtools are raised, the sheet is removed from the recess, turned over, andrelaid in the recess with the unpolished surface uppermost, after'whichthe polishing operation is repeated as above. Handholes 30 arepreferably provided to facilitate lifting the glass sheet from therecess.

A plurality of individual separate recesses similar to the one heredisclosed, might be arranged upon the single table top, tosimultaneously polish several smaller sheets.in stead of one large one.-However, the form here shown is preferable. Since a factory installationincludes a large number of these machines, different groups of machinesmay be provided for different sizes of glass sheets.

The grinding operations which precede the polishing operationsabovedescribed, are preferably performed upon a machine similar.in manyrespects to the one here disclosed. This machine is described in detailand claimed in my copending application, filed of even date herewith.The broader claims to the new apparatus for holding the sheets duringthe surface process without the use of plaster of Paris or other cement,are contained in this companion application, the claims in the presentcase being limited to those features peculiar to the polishing machine.

However, this polishing machine is not limited to use with ground glassblanks produced on the grinding machine noted above. Any flat-groundglass blanks however produced, whose plane surfaces are parallel may bepolished on this machine.

lt is to be understood that in common practice, the machines employedwill embody many auxiliary features not disclosed in this v application,for example, means are provided to automatically raiseand lower thegrinding head when sheets are to be removed or reversed; to stop andstart the machines when the polishing operation is completed,

. and to automatically feed the rouge or other polishing medium to thecontacting surfaces of the sheet and polishing tools duringI thepolishing operation. also provided, to protect the workmen from flyingrouge and possible broken glass, and also to collect the used rouge andwater as thrown from the table. p

Claims:

`l. In an apparatus for polishing` plate glass, in combination, a seriesof polishing tools, and a table having a recess providing a flatsheet-supporting surface, with surroundmg tool-supporting surfaces.

Enclosing means are' 2. The combination with a series of polishingtools, of a supporting Atable for a glass sheet, the table having arecess in its upper face of substantially the same dimensions as thesheet, so that the exposed upper faces of the sheet and table will liesubstantially in the same horizontal plane, and the combined uppersurfaces of the sheet and table being of sufficient extent to supportthe polishing tools throughout their paths of movement.

3. The combination with a series of polishing tools, of a supportingtable for a glass sheet, the table having a recess in its upper face ofsubstantially the same dimensions as the sheet, so that the exposedupper faces of the sheet and table will lie substantially in the samehorizontal plane, the exposed face portions of the table which supportthe polishing members While off from the sheet being formed of a highlypolished metal.

4. In an apparatus for polishing plate glass, in combination, a seriesof polishing tools supported on the glass sheet while in operativeposition, and a supporting table for the sheet, comprising a planesheet-supporting surface, means to support the polishing tools whileofi' from the edges of the glass sheet, the tool-supporting faces ofthis means and of the sheet lying in the same plane, and yieldingabutments intermediate the means and the sheet 'edges to limit lateralmovement of the sheet on thetable.

5. ln an apparatus for polishing plate glass, in combination, a seriesof polishing tools supported on the glass sheet while in operativeposition, and a round sheet-supporting table rotatable about a verticalaxis, the table having a shallow polygonal sheet holding recesssubstantially inscribed within the periphery of the table top, .the sideportions of the table,around the recess, having their upper surfaces inthe same plane as the upper surface of the sheet, to support thepolishing tools While oif from the edges of the sheet.

6. In an apparatus for polishing plate glass, in combination, a seriesof polishing tools supported on the glass 'sheet while in operativeposition, and' a sheet-supporting table having a plane master surfacefor freely supporting the flat groundA glass sheet, this surfaceconforming ,to but being slightly larger than the sheet to be polished,yielding abut-ments for limiting lateral movement of the sheet, andsupporting means for the polishing tools while oil' from the edges ofthe sheet, the tool-supporting surfaces of this means and of the glasssheet lying in substantially the same horizontal plane.

7. In an apparatus for polishing plate glass, in combination, a seriesof polishing tools, supported on the. glass sheet while in operativeposition, and a table having a recess providing a flat sheet-supportingsurface, with surrounding tool-supporting surfaces, the tool-supportingsurfaces of the table and glass sheet when in position, lying in thesame horizontal plane.

8. In an apparatus for polishing plate glass, in combination, a seriesof polishing tools supported on the glass sheet While in operativeposition, and a table having a flat sheet-supporting surface, withsurrounding tool-supporting surfaces, the tool-supporting surfaces ofthe table and glass sheet when in position, lying in the same horizontalplane, the tool-supporting portions of the table being verticallyadjustable to adapt the ap-.

paratus to different thicknesses of plate glass.

9. The combination With a series of polishing tools, of a supportingtable for the glass sheet, the table having a recess in its upper faceof substantially the same dimensions as the sheet, so that the exposedupper faces of the sheetand table will lie substantially in the samehorizontal plane and support the tools throughout their paths ofmovement, and means for vertically adjusting the toolsupporting portionsof the table, to adapt the apparatus for polishing different thicknessesof plate glass.

Signed at Toledo, in the county of Lucas and State4 of Ohio, this 25thday of July, 1923.

JOSEPH P. CROWLEY.

